Oxidation resisting hydrocarbon products



Patented May 15, 1951 OXIDATION RESISTIN G HYDROCARBON PRODUCTS fJohn-G. McNab, Cranford, Niilo V. Hakala, Rahway, and John P. McDermott,Roselle, N. J.,

assignors to Standard Oil Development Company, a corporation of DelawareN Drawing.

Application November 28, 1947, Serial No. 788,670

3 Claims. (Cl. 2 5232.7)

The present invention relates to the improvement of hydrocarbon productsand in particular to the improvementof mineral lubricating oilcompositions by the incorporation therein of a class of additives whichimpart oxidation resist-'- ing properties to such products.

In the development of petroleum lubricating oils the trend has been touse more and more efficient refining methods in order to reduce thetendency of the oils to form carbonand deposits of solid matter or'sludge.- While such highly refined oils possess many advantages, theirresistance to oxidation particularly under conditionsof severe serviceis generally decreased and they are more proneto form soluble'acidicoxidation products which are corrosive. They are generally lesseffective than the untreated oils in protecting the metal surfaces whichthey contact against rusting and corrosion due to oxygen and moisture.They also often deposit thick films of varnish on hot metal surfaces,such as the pistons of internal combustionengines. In accordance withthe present invention a new class of compounds has been discovered,which when added to refined mineral lubricating oils and otherhydrocarbon products in'small portions substantially reduce the tendencyof such products to corrode metal surfaces, particularly the surfaces ofcopper-lead and cadmium-silver bearings which are employed in internalcombustion engines, and they are efiective generally for the purpose ofinhibiting oxidation of hydrocarbon products which are exposed to theaction of atmospheric oxygen. It is well known that many compounds ofcopper, especially certain organic salts such as copper naphthenate, aswell as metallic copper, tend to promote the oxidation of organic.material such as hydrocarbons. Most, if not all, of thecopper compoundshaving this property are cupric, that is, higher valent compounds.-However, it has been found in accordance with the present inventionthat certain cuprous salts, more-specifically the cuprous salts oforgano-thiophosphorio acids, have the property ofinhibiting theoxidation of hydrocarbons to a marked degree.

The class of compounds comprising the antioxidant additives of thepresent invention are more accurately defined as the compounds havingthe general formula where R and R. are hydrocarbon radicals, more freefrom copper staining characteristics.

. 2 specifically alkyl, alkenyl, cycloaliphatic, alkaryl, or aralkylradicals, and in general any radicals, whether aliphatic or aromatic,which contain a total of at least 10 carbon atoms in the combinedaliphatic groups, whether or not attached to aromatic nuclei. In thisspecification and the appended claims the term aliphatic is intended toinclude, both open chain and closed chain groups, saturated orunsaturated, straight chain or branched. The invention also includescompounds of the above type which contain substituted halogen atoms ornitro groups. Compounds of the aliphatic radical type, that is, thosehaving no aromatic nuclei, are generally preferred. In the above generalformula X rep-- resents oxygen or sulfur.

The cuprous salts of the class described above may be readily preparedby treating an organothiophosphoric acid with cuprous oxide, preferablyin the presence of a small amount of a reducin agent, such as sodiumhydrosulfite, which appears to give a product of lighter color and Theorgano-thiophosphoric acid may be prepared by known means, such as byreacting a suitable alcohol with phosphorus pentasulfide;

The preparation of the thiophosphoric acid and its conversion to thecuprous salt may be illustrated by the following equations in which Rrepresents the organic radical of the original alcohol or phenol:

S 4ROH+ P235 2(RO):P 1123 s C1120 2(RO)2P H2O SOu Instead of using asingle alcohol, it is entirely feasible to prepare anorgano-thiophosphoric acid by treating a mixture of two or more alcoholswith phosphorus pentasulfide and'to prepare a cuprous salt useful inaccordance with the present invention by neutralizing the acid productof such a reaction with cuprous oxide. The exact constitution of theacid prepared from a mixture of alcohols is not known, although it isbelieved that the product consists largely of a mixedorgano-thiophosphoric acid containing two different organic radicals. Byemploying mixtures of alcohols it is possible to make use of a certainproportion of short chain alcohols,

since it-is only necessary that the total number of the carbon atoms inthe organic radicals be as great as in order to give the productsufficient solubility in the hydrocarbon base stock.

Instead of alcohols or phenols, mercaptans or thiophenols may beemployed in the original preparation of the thiophosphoric acid. Acidspre pared by the reaction of phosphorus pentasulfide with mercaptans orthiophenols will have sulfur atoms linking the phosphorus atomswith theorganic groups.

Among the alcohols which are generally preferred for use as startingmaterials in the preparation of the salts of the present invention maybe mentioned Z-ethylhexanol, methylcyclohexanol, a commercial mixture of012 to C16 alcohols, alcohols prepared by the reaction of an olefin withcarbon monoxide and hydrogen and subsequent hydrogenation of the productso formed, such as octyl alcohol and nonyl alcohol formed in thismanner, and other products of similar composition and derivation. Theabove are specifically mentioned because of theircommercialavailability, but other alcohols falling within the generalclass described may be employed, such as the normal straight-chainalcohols, alcohols derived from natural waxes, alcohols pro duced by theoxidation of petroleum hydrocarbon products, laur yl alcohol, stearylalcohol, oleyl alcohol, naturally occurring alcohols such as those foundin wool fat, sperm oil, and the like. As discussed above, mixtures ofalcohols may be employed as Well as single alcohols. A mixture ofisop'r'opanol and Z-ethylheXanol is particularly satisfactory.

For the preparation of thiophosphoric acids containing alkaryl groups,'alkyl'a'ted phenols, alkylated naphthols, and the like may be employedin the place of alcohols, and the method is analogous. Preferredexamples of alkylated phenols are amyl phenols, octyl phenols,waxalkylated phenols, petroleum phenols, and like products, includingmixtures of phenols.

For general antioxidant purposes and particularly when the additives areto be employed in mineral lubricating oils, the amount of the additiveswill range from about 0.02% to about 3%, and the particular amount inindividual cases will be selected in accordance with the requirements ofthe case and in view of the properties of the base stock employed. Sincec-uprous org'anothiophosphates prepared from C2 alcohols or higher arecompletely miscible with lubricating oil, it is convenient forcommercial purposes to prepare concentrates containing from '25 to 75%by weight of the additive in mineral lubricating oil, and to transportand blend the additives in the form of such concentrates. Concentratescontaining about 40% of the additive are very conveniently prepared.

The preparation and testing of samples of the additives of the presentinvention as well as samples of analogous salts of other metals forcompari'son are illustrated by the examples to be described in detailbelow, but such examples are not to be construed as limiting the scopeof the invention in any manner.

Example 1.Pr'epa.mtio'n of cup'rou's z-ethylhexyl thiophosph-ate Amixture of 520.8 g. (4 mols) of Z-ethylhexanol and 222 g. (1 mol) ofP285 was heated for 1 hours at 90 C. in a 3-necked, 2-l-iter flaskequipped with a stirrer, reflux condenser and thermometer. The productwas then filtered to remove a small amount of insoluble material.

The thiophosphoric acid was then added dropwise, with stirring, to aslurry of 143 g. (1 mol) of Cu2O and 17.4 g. of sodium hydrosulfite in600 cc. of benzene over a period of 3%, hours (maximum temperature 40C.). After stirring for an additional hour, the product was filtered.The clear dark brown filtrate was mixed with enough "of a light SAE 10grade mineral oil to give as a final product a 40% concentrate. Thissolution was then placed on a steam bath with nitrogen blowing for 24hours to remove the benzene and water. Upon analysis, this concentratewas found to contain 5.8% copper and 5.7% sulfur; theoretical valueswere 6.1% copper and 6.1% sulfur.

Emmple 2.-Preparation of cuprous nonyl thiophosphate This preparationwas carried out in the same manner as that described in Example 1, using576 g. of nonyl alcohol (a branched chain C9 alcohol prepared byreacting diisobutyl'ene, carbon monoxide and hydrogen and hydrogenatingthe product), 222 g. of P235, 143 g. of 01120, and 17.4 g. of sodiumhydro'sulfite.

Upon analysis, the 40% oil concentrate was found to contain 6.3% copperand 7.0% sulfur; theoretical values were 6.3% copper and 6.4% sulfur.

Example 3-. Prepcmt'iovz of cuprous bowl rhiophos hate A mixture of 520g. (4 mols) of octyl alcohol (a branched chain Ga alcohol prepared byreacting a C1 olefin polymer, carbon monoxide and hydrogen andhydrogenating the product), and 222 g. (1 mol) of P285 was heated for 1hours at C., in a -3-necked, -2-liter flask equipped with a stirrer,reflux condenser, and thermometer. The thiophosphoric acid was thenpoured into a 4- liter beaker containing 1126 g. of diluent oil (a lightlubricating oil of approximately SAE 10 grade). With rapid stirring andnitrogen blowing, a mixture of 17.4 g. of sodium hydrosulfite and 128.7g. of CuzO was added in small portions over a period of about 50minutes, during which time the temperature rose from 40 C. to 55 C.After stirring for an additional 1.5 hours at C., the product wasfiltered. Aclear, dark brown concentrate was obtained, which uponanalysis was found to contain 5.6% copper, 3.1% phosphorus and 6.5%sulfur.

Example '4.P1epd'rdtiofi of cuprous methylcycZohEti Z thiophospha'te A3-'necked, 1-'-'-litefr flask, equipped with a stirrer, reflu-xcondenser and thermometer, was charged with 228 g. (2 mols) ofinethylcyclohexa'nol 'and 111 g. mol) or'rzss. This mixture was heatedwith stirring at C., 'for 30 minutes, after which the resultingthiophosphoric acid was poured into a 3-li'ter beaker containing 514 g.of a light lubricating {oil of approximately SAE '10 grade. Thissolution was then heated to 50 C., after which 7 g. /2 mol) of C1120 wasadded in small portions over a period of 30 minutes with rapid stirringa'ndnitrogen blowing (temperature rose to 90 0.). Afterstirring for anadditional twenty minutes at 110 C., the product was filtered, a clear,dark red, viscous concentrate being obtained. Upon analysis it was 3.4%phosphorus.

Example 5.--Prep'aiation of cuproas isopropyl ethylheryl thiophosphateThe isoprcpyl-ethylhexyl thiophosphoric acid mixture was prepared asdescribed in Example 1, using a mixture of 907g. (1.5 mol) ofisopropanol and 130 g. (1 mol) of ethylhexanol. The acid mixture waspoured into 561 g. of a light lubri cating oil of approximately SAEgrade, and after heating to 50 0., 88.7 g; of C1120 was added in smallportions over a period of about 30 minutes. After stirring for anadditional 2 hours at 105 C., with nitrogen blowing, the product-wasfiltered, a clear, deep red concentrate being obtained, which uponanalysis was foundqto contain 7.3% copper, 7.4% sulfur, and 3.7%phosphorus, indicating the product to be a 40% oil concentratecontaining cuprous isopropyl thiophosphate, cuprous ethylhexylthiophosphate and/or the cuprous salt of mixed isopropyl-ethylhexylthiophosphoric acid. This concentrate remained clearafter standing for 2weeks at 30 F.

Example 6.Preparatz'on of cuprous ClZ-Clfi alkyl-seconolary batylthiopho'sphate This preparation was carried out in the same manner asthat described in Example 5, using a Example 7.Preparation of calciumethylhezcyl thiophosphate The ethylhexyl thiophosphoric acid wasprepared as described in Example 1. The calcium salt was then preparedin the same manner as described in Example 5, using CaO as theneutralizing agent.

Example 8.Preparatzon of potassium ethylheryl thiophosphate Thispreparation was carried out in the same manner as that described inExample 7, using KOH as the neutralizing agent. Upon cooling thisconcentrate to room temperature, a considerable amount of the potassiumsalt precipitated out of solution.

Example 9.--Preparation of sodiumpthylhexyl thiophosphate v Thispreparation was carried out in the same manner as that described inExample 7, using NaO-H as the neutralizing agent.

Example 10.--Preparation of zinc ethylhea cyl thiophosphate Thispreparation was carried out in the same manner as that described inExample 7, using ZnO' as the neutralizing agent.

Example 11.Laboratory bearing corrosion tests Blends containing 0.25%each of various 011-, prous salts prepared as described in precedingexamples in an extracted Mid-Continent lubrieating oil of parafiinic SAE20 grade and a sample of the unblended base oil were submitted to alaboratory test 'designedto measure the;

efiectiveness of the, new additives in inhibiting the corrosiveness of atypical mineral lubricating oil toward the surfaces of copper-leadbearings. The test was conducted as follows:

500 cc. of the oil was placed in a glass oxidation tube (13 inches longand 2% inches in diameter) fitted at the bottom with a A; inch air inlettubeperforated to facilitate air distribution. The oxidation tube wasthen immersed in a heating bath so that the oil temperature wasmaintained at 325 F. during the test. Two quarter sections of automotivebearings of copper-lead alloy of known weight having a total area of 25sq. cm. were attached to opposite sides of a stainless steel rod whichwas then immersed in the test oil and rotated at 600 R. P. M1, thusproviding suficient agitation of the sample during the test. Air wasthen blown through the oil at the rate of 2 cu. ft. per hour. At the endof each 4-hour period the bearings were removed, washed with naphtha andweighed to determine the amount of loss by corrosion. The hearings werethen repolished (to increase the severity of the test), reweighed, andthen subjected to the test for additional 4-hour periods in like manner.The results are given in the following table as corrosion life, whichindicates the number of hours required for the bearings to lose mg. inweight, determined by interpolation of the data obtained in the variousperiods.

Bearing Corroslon Life, Hrs.

Oil Blend Example 12.Lauson engine tests Blends containing 0.6% each ofvarious products prepared as described in the foregoing examples in asolvent extracted Mid-Continent parafiinic lubricating oil of SAE 10grade and a sample of the unblended base oil were employed as crankcaselubricants in tests with a Lauson engine operating at 300 F. jackettemperature, 295 F. oil temperature, 1800 R. P. M. speed, and 1.5indicated kilowatt load, the tests being conducted for 20 hours each.The loss in weight of the copper-lead bearing and the varnish demeritwere determined in each test. The varnish demerit rating was based upona method of rating in which a perfectly clean piston surface is given arating of 0 and a demerit of 10 is given to the worst condition whichcould be expected to exist of that surface. The results of theseobservations are as follows:

Bearing Weight Varnish Base 011 Loss (Mg./

Demeut Bearing) Base oil u 3. 5 220 Base oi1+0.6% cuprous ethylhexylthiophosphate (Ex. 1) 1. 5 20 Base oil+0.6% calcium ethylhexylthiophosphate (Ex. 2. 8 37 Base oil+0.6% potassium ethylliexylthiophosphate (Ex. 8) 4. 3 19 Base oil+0.6% sodium ethylhexyl thio- 7phosphate (Ex. 9) 6.0 32

E xampZe 13.C'hevrolet engine tes'ts Blends containing products ofvarious preceding examples in a solvent extracted Mid-Continentparafilnic SAE oil in the amounts indicated below and a sample of theunblended base oil were employed as the crankcase oil in 36-hour testswith a Chevrolet engine operated at 30 brake H. P., 3150 R. P. M. speed,280 F. oil temperature and 200 F. jacket temperature. After each testwas completed, the weight loss of the copper-lead bearing wasdetermined. The results are shown in the following table:

The above data indicate clearly that the additives of the presentinvention are very effective in reducing bearing corrosion as well asbeing somewhat effective in also reducing varnish formation on thepiston surface. It may also be observed that the cuprous salts aregenerally more effective than the alkali metal salts. Although thepotassium ethylhexyl thiophosphate reduced the bearing corrosion to thesame extent as the corresponding cuprous salt in the Lauson engine test,it will be observed that the potassium salt caused a greater amount ofvarnish formation than the unblended base oil, while the cuprous saltreduced the varnish formation.

The new additives of the present invention, while effective ininhibiting bearing corrosion, do not always inhibit the tendency of theoil to deposit varnish on engine parts to the desired .extent, and it isaccordingly advantageous to employ in combination with these additivesother additives which have a detergent action. Among the most useful ofsuch detergent additives are metal phenates, sulfurized metal phenates,.sulfurized metal salts of phenol sulfides, reaction products .of metalphenates and metal salts of phenol sulfide with sulfides of phosphorus,metal carboxylates, metal sulfonates, and the like. The followingexample illustrates the advantages realized in employing a combination.of additives.

Example '14.Chem'oZet engine tests of additive combinations inlubricating oil Blends were prepared containing cu-prous ethylhexylthiophosphate (prepared as in Example 1) alone and in combination withcertain detergent additives as shown in the table below. Tests were alsomade of the base oil, which was a solvent extracted Mid-Continentparaflinic SAE 10 oil which was of a different lot and higher sulfurcontent from the oil employed in the tests of Example 13. Tests werealso made with a blend of this oil with a typical detergent additivealone. The tests were conducted in the manner described in Example 13,while the varnish demerit ratings were made according to the systemdescribed in Example 12. The results of these tests are as follows:

v h n sarms 111g elg O11 Blend Demerit Loss (GmJ Bearing) phosphateu nnv 3. 79 0. 09 Base oil+0.7-% barium tert.-octyl phenol sulfide -P;reaction product. 0. 35 O. 65 Base oil+0.l8% cuprousIethylhexylthiophenol sulfide-R 85 reaction product. 0.88 Q. 16 Base oil-H).5l5%cuprous ethylhexyl thiophosphate+0.5% calcium petroleum The above datashow that extremely good results are obtained from the combination ofthe cuprous alkyl thiophosphate and the barium octylrphenol sulfide-Passreaction product, with regard to both varnish demerit and bearingcorrosion.

The products of the present invention may be employed not only inordinary hydrocarbon lubricating oils but also in the heavy duty type rof lubricating oils which have been compounded with such detergent typeadditives as metal soaps, metal petroleum sulfonates, metal phenates,metal alcoholates, metal alkyl phenol sulfides, metal organo phosphates,thiophosphates, phosphites and thiophosphites, metal salicylates, metalxanthates and thioxanthates, metal thiocarbamates, amines and aminederivatives, reaction products of metal phenates and sulfur, reactionproducts.

of metal phenates and phosphorus sulfides, metal phenol sulfonates andthe like. Thus the additives of the present invention may be used inlubricating oils containing such other addition agents as bariumtert.octy1phenol sulfide, calcium tert.-amylphenol sulfide, nickeloleate, barium octadecylate, calcium phenyl stearate, zinc .diisopropylsalicylate, aluminum naphthenate, calcium cetyl phosphate, bariumdi-tert.-amylphenol sulfide, calcium petroleum sulfonate, zinc methylcyclohexyl thiophosphate, calcium dichlorostearate, etc. Other types ofadditives, such as phenols and phenol sulfides may be employed.

The lubricating oil base stocks used in the compositions of thisinvention may be straight mineral lubricating oils or distillatesderived from parafiinic, naphthenic, asphaltic, or mixed base crudes,or, if desired, various blended oils may be employed as well asresiduals, particularly those from which asphaltic constituents havebeen carefully removed. The oils may be refined by conventional methodsusing acid, alkali and/or clay or other agents such as aluminumchloride, or they vmay be extracted oils produced, for example, bysolvent extraction with solvents of the type of phenol, sulfur dioxide,furfural, dichlorodiethyl ether, nitrobenzene, crotonaldehyde, etc.Hydrogenated oils or white oils may be employed as well as syntheticoils prepared, for example, by the polymerization of olefins or by thereaction of oxides of carbon with hydrogen or by the hydrogenation ofcoal or its products. In certain instances cracking coil tar fractionsand coal tar or shale oil distillates may also be used. Also, forspecial applicatiens, animal, vegetable or fish oils or theirhydrogenated or yoltolized products may be employed in admixture withmineral oils.

For the best results the base stock chosen should normally be that oilwhich without the new additive present gives the optimum performance inthe service contemplated. However,

since one advantage of the additives is that their use also makesfeasible the employment of less satisfactory mineral oils or other oils,no strict rule can be laid down for the choice of the base stock.C'ertain essentials must of course be observed. The oil must possess theviscosity and volatility characteristics known to be required for theservice contemplated. The oil must be a satisfactory solvent for theadditive, although in some cases auxiliary solvent agents may be used.The lubricating oils, however they may have been produced, may varyconsiderably in viscosity and other properties depending upon theparticular use for which they are desired, but they usually range fromabout 40 to 150 seconds Saybolt viscosity at 210 F. For the lubricationof certain low and medium speed Diesel engines the general practice hasoften been to use a lubricating oil base stock prepared from naphthenicor aromatic crudes and having a Saybolt viscosity at 210 F. of 45 to 90seconds and a viscosity index of to 50. However, in certain types ofDiesel engine and other gasoline engine service, oils of higherviscosity index are often preferred, for example, up to 75 to 100, oreven higher, viscosity index.

In addition to the material to be added according to the presentinvention, other agents may also be used such as dyes, pour depressors,heat thickened fatty oils, sulfurized fatty oils, organometalliccompounds, metallic or other soaps, sludge dispersers, antioxidants,thickeners, viscosity index improvers, oiliness agent, resins, rubberolefinpolymers, voltolized fats, voltolized mineral oils, and/orvoltolized waxes and colloidal solids such as graphite or zinc oxide,etc. Solvents and assisting agents, such as esters, ketones, alcohols,aldehydes, halogenated or nitrated compounds, and the like may also beemployed.

Assisting agents which are particularly desirable as plasticizers anddefoamers are the higher alcohols having eight or more carbon atoms andpreferably 12 to 20 carbon atoms. The alcohols may be saturated straightand branched chain aliphatic alcohols such as octyl alcohol (CsHrzOH)lauryl alcohol (C12H25OH), cetyl alcohol (CmHasOI-I) stearyl alcohol,sometimes referred to as octadecyl alcohol, (UmHsvOI-I), heptadecylalcohol (C17H35OH), and the like; the corresponding olefinic alcoholssuch as oleyl alcohol; cyclic alcohols such as naphthenic alcohols; andaryl substituted alkyl alcohols, for instance, phenyl octyl alcohol, oroctadecyl benzyl alcohol; or mixtures of these various alcohols, whichmay be pure or substantially pure synthetic alcohols. One may also usemixed naturally occurring alcohols such as those found in wool fat(which is known to contain a substantial percentage of alcohols" havingabout 16 to 18 carbon atoms) and in sperm oil (which contains a highpercentage of cetyl alcohol) and although it is preferable to isolatethe alcohols from those materials, for some purposes the wool fat, spermoil or other natural products rich in alcohols may be used per se.Products prepared synthetically by chemical processes may also be used,such as alcohols prepared by the oxidation of petroleum hydrocarbons, e.g. paraffin wax, petrolatum, etc.

In addition to being employed in crankcase lubricants the additives ofthe present invention may also be used in extreme pressure lubricants,engine flushing oils, industrial oils, general machinery oils, processoils, rust preventive compositions and greases.

The additive of the present invention may be employed as antioxidant orstabilizing agents not only in mineral lubricating oils, but also inpetroleum hydrocarbon products generally, where improved resistance tooxidation is desired. Thus the products may be added to motor oils,Diesel fuels, kerosene, waxes, hydrocarbon polymers, natural andsynthetic rubbers, and the like.

The present invention is not to be considered as limited by any of theexamples described herein, which are given by way of illustration only,but is to be limited solely by the terms of the appended claims.

We claim:

1. A composition consisting essentially of a hydrocarbon oil containing0.02 to 3% of a compound of the approximate formula the reaction productof the barium salt of tert.- octyl phenol sulfide and phosphoruspentasulfide.

JOHN G. MCNAB.

NIILO V. HAKALA.

JOHN P. MCDERMOT'I.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,261,047 Assifi Oct. 4, 19412,364,154 Denison Apr. 11, 1944 2,364,283 Freuler Dec. 5, 1944 2,378,820Amott June 19, 1945 2,389,527 McCleary Nov. 20, 1945 2,420,893 McNab gMay 20, 1947

1. A COMPOSITION CONSISTING ESSENTIALLY OF A HYDROCARBON OIL CONTAINING 0.02 TO 3% OF A COMPOUND OF THE APPROXIMATE FORMULA 